Pressure gauge spring

ABSTRACT

The pressure gauge spring is a responsive and easy to manufacture gauge for connection to a pressure source. The spring assembly comprises a coiled hollow tube having a first end and a second end with a body portion therebetween, the hollow tube adapted to produce a displacement of the second end in response to a change in said pressure source to which said first end is connected. The second end of the body portion is sealed. The body portion of the spring assembly has a first longitudinal portion and a second longitudinal portion extending from proximate to said first longitudinal portion to said second end and substantially uniformly compressed along the second longitudinal portion to reduce volume thereby. A transition area is disposed between said first end and said first longitudinal portion of said hollow tube, and is compressed so as to form a continuous longitudinally extending ridge along said transition area.

FIELD OF THE INVENTION

[0001] The invention relates generally to pressure gauges and moreparticularly to bourdon tube pressure gauges.

BACKGROUND OF THE INVENTION

[0002] Spring gauges for use in measuring pressure or temperature arewell known and have been used commercially for many years. In the caseof a Bourdon tube gauge, the measurement element is a tube sealed at afirst end and attached to a pressure source to be measured at a secondend. U.S. Pat. No. 4,667,517 discloses a Bourdon tube spring element formeasuring pressure. Generally, such gauges offer a multitude of usesincluding applications in the fire protection, medical component, andacetylene welding industries. The spring element is made by compressingthrough cold working only predetermined areas of a tube wall resultingin a relatively less compressed ridge extending along the length of thetube. This ridge facilitates rapid communication of changes in thepressure source along the length of the tube. Accordingly, response timeof the gauge is improved. Unfortunately, the spring gauge requirescareful cold working along the entire length of the tube by compressionto form the ridge and fails to minimize the volume within the tube andthe materials required to produce it.

SUMMARY OF THE INVENTION

[0003] The invention provides a bourdon tube gauge for measurement ofpressure with improved responsiveness to pressure fluctuations, ease ofmanufacture, and reduced material requirements as compared toconventional pressure gauges. The pressure gauge of the inventionincludes a spring assembly for connection to a pressure source includinga coiled hollow tube having a first end and a second end with a bodyportion therebetween. The hollow tube is adapted to produce adisplacement of the second end in response to a change in the pressuresource to which the first end is connected. The second end of the bodyportion is sealed. The body portion of the spring assembly has a firstlongitudinal portion and a second longitudinal portion extending fromproximate to the first longitudinal portion to the second end. The bodyportion is substantially uniformly compressed along the secondlongitudinal portion to thereby reduce the volume of the body portion.

[0004] In one embodiment, a transition area is disposed between thefirst end and the first longitudinal portion of the hollow tube. Thetransition area is compressed in a manner so as to form a continuouslongitudinally extending ridge along said transition area. In anotherembodiment, the second longitudinal portion is substantially uniformlycompressed to form a uniform thickness along the length thereof. Thefirst longitudinal portion and the transition area are partiallycompressed so as to form a ridge extending along the length of thetransition area and the first longitudinal portion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is an enlarged plan-view of a spring element according tothe invention;

[0006]FIG. 1A is a cross-sectional view through line A-A′ in FIG. 1;

[0007]FIG. 1B is a cross-sectional view through line B-B′ in FIG. 1;

[0008]FIG. 1C is a cross-sectional view through line C-C′ in FIG. 1;

[0009]FIG. 2A is a perspective view of a spring element constructed inaccordance with the invention in the extended configuration; and

[0010]FIG. 2B is a perspective view of the spring element of FIG. 2A ina coiled configuration.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0011]FIGS. 1, 1A, 1B, 1C and FIGS. 2A, 2B, depict a spring assembly fora pressure gauge comprising a hollow tube having a first end 10, asecond end 15 and a body portion 20 therebetween. When in use in thepressure gauge, the tube is coiled from first end 10 to second end 15.The body portion is compressed to form a transition area 25 disposedproximate to first end 10, a first longitudinal portion 30, and a secondlongitudinal portion 35. In one embodiment, the length of the firstlongitudinal portion 30 is 5 to 10 percent of the length of the secondlongitudinal portion 35. The first longitudinal portion 30 extends fromthe transitional area 25 to the second transitional portion 35. Thesecond transitional portion 35 extends from the first transitionalportion 30 to the second end 15 of the body portion 20. First end 10 ofbody portion 20 is adapted for mounting to a pressure source and secondend 15 of body portion is fitted with an indicator pointer 45 as shownin FIG. 2B.

[0012] With continued referenced to FIGS. 1, 1A, 1B, 1C, firstlongitudinal portion 30 (FIG. 1B), and second longitudinal portion 35are substantially uniformly compressed to form a uniform thickness alongthe length of first and second longitudinal portions 30, 35 and thetransitional area 25 (FIG. 1A) is partially compressed so as to form aridge 40 (FIG. 1A) in one embodiment of the invention. In anotherembodiment, second longitudinal portion 35 is substantially uniformlycompressed so as to form a uniform thickness along the length of secondlongitudinal portion 35. Both the first longitudinal portion 30 and thetransition area 25 are partially compressed so as to form a ridge 40extending along the length of the first longitudinal portion 30 and thetransition area 25.

[0013] In one embodiment, body portion 20 comprises a thin-walled steeltube longitudinally coiled into a spiral. In other embodiments, bodyportion 20 comprises a thin-walled steel tube longitudinally coiled intoa planar helix.

[0014] In operation pressure from the source being measured is appliedto the first end 10 and causes the fluid (such as, for example, air) toexpand into the first longitudinal portion 30 and the secondlongitudinal portion 35. The pressure of the fluid causes the tube inthe coiled configuration (see FIG. 2B) to uncoil as a known function ofthe applied pressure at the first end 10. As more pressure is applied,the more the coil uncoils, thereby causing the indicator 45 to move to adifferent location on a calibrated dial. The ridge 40 permits the fluidto enter the longitudinal portions 30, 35 more uniformly and rapidly.

[0015] With renewed referenced to FIG. 2B, the spring assembly ismanufactured by first bending the body portion 20 of the tube at thetransitional area 25 to form a substantially right angle withlongitudinal portions 30, 35. The remainder of the spring assembly, fromthe transition area 25 to the second end 15 is substantially flatten byusing known metal working methods, for example, by feeding the bodyportion 20 between two opposing compression wheels. If compressionwheels are used for manufacturing the spring assembly, an arc portionwith a length matching the ridge 40 is recessed along the circumferenceof both of the wheels to substantially reduce the compression of thebody portion 20 along the transition area 25 as the body portion 20feeds between the wheels and so as to form the ridge 40 along thetransition area 25. The remaining areas of the wheels are substantiallyuniform and accordingly, the first longitudinal portion 30 and thesecond longitudinal portion 35 are substantially uniformly compressed.

[0016] In one embodiment the spring assembly, prior to coiling, is heattreated at temperature between 600 and 800 degrees Fahrenheit forbetween 1 and 3 hours to improve tensile strength and gaugeresponsiveness. In a further embodiment or in combination with theaforementioned embodiment, the spring assembly is processed in an acidwash solution wherein the acid wash solution comprises 25 percentphosphoric acid, 75 percent water, and a brass plate for 30 to 60minutes.

[0017] The invention may be embodied in other specific forms withoutdeparting form the spirit or essential characteristics thereof. Theforegoing embodiments are therefore considered in all respectsillustrative rather than limiting of the invention described herein.Scope of the invention is thus indicated by the appended claims ratherthan by the foregoing description, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced herein.

What is claimed is: 1-10 (Canceled)
 11. A spring assembly for a pressuregauge for connection to a pressure source, the spring assemblycomprising: a coiled hollow tube having a first end and a second endwith a body portion therebetween, the hollow tube adapted to produce adisplacement of the second end in response to a change in the pressuresource to which the first end is connected; the body portion having asubstantially cylindrical portion extending from proximate the firstend, a first longitudinal portion, and a second longitudinal portionextending from proximate the first longitudinal portion to the secondend, the second longitudinal portion substantially uniformly compressedto reduce volume thereby; a transition area defined by the regionbetween the substantially cylindrical portion and the secondlongitudinal portion of the hollow tube, the transition area beingcompressed so as to form a continuous longitudinally extending ridgealong the transition area; and wherein the second end of the bodyportion is sealed.